This invention relates to flat panel display terminals. Examples of flat panel display terminals are electroluminescence, liquid crystal displays ("LCDs") and plasma or gas-discharge displays. More particularly, the invention relates to interfaces of LCDs for simulating the operations of multifrequency cathode-ray tube ("CRT") monitors.
Flat panel technology has been encouraging as of the late 1980s, particularly for buyers not concerned with cost. Many advantages of the flat panel display terminals are known over the CRT type monitors which have enjoyed almost universal application in personal computers. For example, an LCD monitor provides advantages including a flat surface, inherent sharpness, low power consumption, less eye-strain on the user and compact size. The flat surface of an LCD also eliminates problems associated with the convex surface of a CRT screen such as undesirable curved lines and distorted images near the edges of the CRT screen. With their compact size, low-power usage and light weight, LCDs have been used typically in laptop computers and seatback televisions on aircraft.
With the introduction of high-quality and low-price LCD models, the computer industry has taken a closer look at flat panel display terminals for use in desktop computers and workstations. Since most computers produce video signals appropriate for the CRT monitors, attempts have been made to develop controllers or converters to resolve the differences between the CRT monitors and the LCDs. For example, the LCDs are chemically operative systems whereas the CRT monitors are electrically operative systems. The converters, thus, need to address a slower response time of the LCDs. Also, while the CRT monitors can display any number of horizontal and vertical lines, the LCDs have a set number of horizontal and vertical lines. The converters need to deal with such limitations as well.
Additional concern for LCD use in a desktop computer is the physical distance between the LCD panel and the graphic board. Direct connections between the graphic controllers and the LCDs are possible in laptop computers where LCDs are closely positioned to graphic controllers within the same computer chassis. LCDs having parallel RGB interfaces, therefore, can directly receive the RGB signals provided by the graphic controllers.
However, for desktop computers, the graphic controllers are generally located inside the computer chassis while the RGB interfaces are located in separate monitors. The RGB signal outputs from the graphic controllers, therefore, are provided indirectly via video cables connecting the graphic boards of the desktop computers and the LCDs. Since standard desktop computers produce analog RGB signals for cable connections instead of digital video signals, digital LCDs need additional analog to digital converters ("ADCs") to interpret the video signals from the desktop computers. Such conversions negatively effect the resulting screens due to the difficult timing and complications associated with the conversions.
In response to such complications, analog LCDs that are capable of utilizing analog RGB signals have been introduced to the market recently. Although such analog LCDs do not require ADCs, the currently available interfaces either require stacks of boards or are incapable of any high-level functions. For example, even though analog LCDs allow multiple resolutions such as VGA, SVGA, XGA, TEXT 1 and TEXT 2, the currently available interfaces for the analog LCDs cannot compensate for inaccuracies or offsets that accompany the video signals primarily directed for the CRT monitor use.
It is therefore an object of this invention to provide simplified, sophisticated, effective and inexpensive apparatus for flat panel display terminals. More particularly, it is an object of this invention to provide an interface that allows analog LCDs to simulate the operations of multifrequency CRT monitors having capabilities to adjust to various display protocols.